If you absolutely 100% for sure have to use resource forks, find a way not to. Make a converter to extract the resource fork data and save it into a separate data file before use if you have to. You must access resource forks through Carbon (that is, if there are even any resource manager routines left lying around; I haven't touched them in years myself). Do not ever attempt to write your own resource fork parser. 1) it's a complete waste of effort 2) it is virtually impossible to do correctly.

Inside Macintosh had a description of the format of the resource fork, but I really suggest just using the Carbon Resource Manager. It's not all that hard, and is sure as heck easier than writing your own